Snap hooks are very common items of fishing tackle. They are used wherever disengagable connections are needed, such as in the attachment of hooks and lures to swivels, or in connecting any of these components directly to a fish line or leader. They are easily formed from spring steel wire, and must be of sufficient strength to withstand all of the forces normally applied to the fish line. They are preferably as small as possible, which produces a corresponding problem with respect to the limitation on resilience resulting from the desirable small size. Connecting and disconnecting these hooks can be a real problem, if unduly large forces are required. Adverse weather conditions will frequently result in decreasing a fisherman's dexterity with his fingers, as well as interfering with his vision. Preferably, these little devices should be engagable and disengagable entirely through a sense of touch, and with low enough forces involved that it does not become a feat of strength.
Some of the standard forms of snap hooks currently available include one form vaguely resembling a safety pin, in which one tail of a spring coil is provided with a hood receiving the opposite tail, which is bent into a bight. Since this configuration requires a combination of wire-bending, sheet metal forming, and the assembly of these components, the cost become a problem. Another common form of snap hook is essentially a double loop of wire, with the larger loop being a bight with a hook at its end engagable with a small fixed loop at the opposite end of the device. While the fixed loop connection considerably increases the strength of the snap hook, it eliminates all of the resilience at that end of the device. The only effective remaining resilience is provided by the bight as it extends from the point of fixed connection to the point of disengagement.